Chromatographic pumping method

ABSTRACT

To provide smooth constant flow from a pump, a chromatographic system comprises: a chromatographic column having an inlet; a pump for supplying fluid to the inlet of the chromatographic column; a power means for the pump motor; positive and negative feedback loop means for controlling said power means; means for energizing and de-energizing said positive and negative feedback control means; said negative feedback control means receiving a signal from said means for measuring flow rate and including means for comparing said signal with said corrected flow rate reference signal while said second feedback loop is energized to generate an error signal controlling said power means; and said positive feedback control means applying an acceleration voltage to said motor from a time a preset period after the initiation of a return stroke of said piston until after a timed duration.

REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 07/099,387for Chromatographic Pumping System, filed by Robert W. Allington onSept. 21, 1987, now U.S. Pat. No. 4,869,374, which is a division of U.S.application Ser. No. 06/838,295 filed Mar. 10, 1986, now U.S. Pat. No.4,733,152 and both are assigned to the same assignee as thisapplication.

BACKGROUND OF THE INVENTION

This invention relates to reciprocation pumps and control circuits forthem.

In one class of reciprocating pump, a piston continuously reciprocatesin a cylinder to directly force a liquid from the cylinder, alternatelypulling liquid into the cylinder through an inlet port from a reservoirand pushing it from the cylinder through an outlet port to thedestination of the liquid.

In some uses of this class of pump, the pumps are designed to reducepulsation in the flow of fluid. One such use is liquid chromatography.It is desirable in liquid chromatography that liquid which is pumpedthrough a chromatographic column flow at a constant flow rate throughthe column so that different molecular species in the effluent from thecolumn are eluted at times that are reproducible from run to run. Pulsesin which the liquid flows at unpredictable rates reduce thisreproducibility.

In one type of prior art pump of this class, the pressure at the outletport of the pump is measured by a pressure sensor. A feedback signalfrom the pressure sensor controls the speed of the pump motor to causethe pump motor to react to changes in pressure in the chromatographiccolumn and thus maintain a more constant rate of flow of the fluid. Onepump of this type is described in U.S. Pat. No. 3,985,467, issued Oct.12, 1976 to Peter Lefferson.

This type of pump has a disadvantage when used in liquid chromatographyin that it maintains pressure constant against varying pressure loadsbut may cause the rate of flow of fluid through the chromatographiccolumn to vary, even in applications where it is desirable to maintainthe rate of flow of liquid constant.

In another type of prior art pump of this class, the piston is driven ata constant rate while expelling liquid from the pump into thechromatographic column, but when returning on a fill stroke to drawfluid into the pump from the reservoir, the motor is driven at anincreased and substantially constant speed to draw the fluid into thepump more rapidly.

During the forward stroke of piston in this type of prior art pump, thepiston moves at a higher than normal rate until the pressure in the pumpcylinder equals the pressure that existed near the end of the liquidexpelling foward stroke of the piston and just before the piston began arefill stroke. After the pressure in the cylinder reaches the pressureduring constant flow rate pumping before the start of the refill stroke,the outlet valve is opened and the piston continues foward at a constantrate. This type of pump is described in U.S. Pat. No. 4,131,393 issuedDec. 26, 1978, to Haaken T. Magnussen Jr. and U.S. Pat. No. 4,180,375issued Dec. 25, 1979 to Haaken T. Magnussen Jr.

This type of pump has several disadvantages such as for example: (1) theopening of the valve at the pressure of the last part of the previouscycle results in an increased time during which no liquid leaves theoutlet port over that time needed to fill the cylinder; (2) the constantspeed of the motor during refill and pump up does not reduce the timebefore fluid leaves the pump as soon as it could; (3) the pump isrelatively uncomplicated because the acceleration time of the motor istime-limited rather than distance limited; (4) the pump is able toaccomodate a wider range of flow rates without cavitation; (5) the pumpmotor maintains a constantly changing velocity during the refill portionof a cycle and a portion of a delivery stroke of the piston; (6) theaverage flow rate is continuously monitored and adjusted by adjusting acurrent input signal representing the preset flow rate of fluid; and (7)the velocity of the motor is increased to accomodate high pressure andhigh flow rates without long periods necessary to replace liquid lastduring a refill portion of a pumping cycle.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a novel pump.

It is a further object of the invention to provide a novel method forpumping fluid in a manner that maintains a constant rate of flow offluid through a chromatographic column spaced from the outlet of thepump.

It is a still further object of this invention to provide a pumpingtechnique in which the speed of the motor is constant during a secondportion of a pumping stroke until a refill portion of a cycle isinitiated and then continuously increasing in speed during refill anduntil after a first portion of the pumping stroke controlled in timeduration.

It is a still further object of this invention to drive a pump motor fora reciprocating pump at a constant rate during a first portion of acycle with a feedback circuit and at an accelerating rate during asecond portion controlled by a timer and an open loop control circuit.

It is a further object of the invention to maintain average rate of flowconstant.

It is a still further object of this invention to provide areciprocating pump for a chromatographic system in which the pump refilltime is maintained as short as possible and liquid is pumped in such amanner as to prevent cavitation but increase the rate of flow of fluidtemporarily to maintain as constant as possible from cycle to cycle theaverage amount of liquid pumped through the liquid chromatographiccolumn.

It is a still further object of the invention to cause a smoothacceleration of pumping for a time after a refill stroke to reduce thedanger of cavitation but maintain the flow rate at the column asconstant as possible.

In accordance with the above and further objects of the invention, thespeed of a motor which drives a direct displacement reciprocating pumpis controlled by first and second related signals. These signals arerelated so that a high constant rate of pumping controlled by the firstsignal results in a high rate of acceleration of the pumping actionlater under the control of the second signal to more quickly average theflow rate to the preset flow rate of the liquid after a refill portionof a pump cycle.

The first signal provides a linear feedback control on the pumpingmotion of a piston during a time period in which the rate of flow ofliquid from the pump is equal to a preset rate of flow and the pistonmoves at a present velocity. The second signal is a nonlinear positivefeedback signal which accelerates the motor linearly through an openloop to pull liquid from the liquid reservoir as fast as possiblewithout cavitation and to provide liquid without cavitation to theoutlet port of the pump at a rate to replace in the conduit to thechromatographic column the liquid necessary to bring the average rate offlow back to the preset value with little interruption to fill thecylinder. Thus, the piston is driven in a continuously varying rateexcept for a portion of a pump cycle.

A second feedback loop within which the first and second signals operatemeasures the flow rate from the pump and corrects the preset rate offlow current source to maintain the average flow rate over a pump cycleconstant.

From the above description, it can be understood that the pump of thisinvention has several advantages such as: (1) the time during which noliquid is pumped through the outlet port is low; (2) it is relativelyuncomplicated because the acceleration time of the motor is time limitedrather than distance limited; (3) it is able to accomodate a wide rangeof flow rates without cavitation; (4) it maintains an acceleratingvelocity during a first part of each pumping stroke related to therequired liquid to be replaced; and (5) it repeatedly monitors rate offlow and corrects the input signal outside of the feedback loop to aidin maintaining average flow constant.

SUMMARY OF THE DRAWINGS

The above noted and other features of the invention will be betterunderstood from the following detailed description when considered withreference to the accompanying drawings in which:

FIG. 1 is a block diagram of a chromatographic system utilizing anembodiment of the invention;

FIG. 2 is a block diagram of a control system for a high pressure pumpin the chromatographic system of FIG. 1 in accordance with an embodimentof the invention;

FIG. 3 is a block diagram of a motor circuit for a pump in accordancewith the embodiment of FIG. 2;

FIG. 4 is a schematic circuit diagram of a portion of the motor controlcircuit of FIG. 3;

FIG. 5 is a schematic circuit diagram of another portion of the motorcontrol circuit of FIG. 3;

FIG. 6 is a schematic circuit diagram of still another portion of themotor control circuit of FIG. 3;

FIG. 7 is a schematic circuit diagram of still another portion of themotor control circuit of FIG. 3;

FIG. 8 is schematic circuit diagram of another portion of the motorcontrol circuit of FIG. 3;

FIG. 9 is a block diagram of a portion of the circuit of FIG. 2;

FIG. 10 is a block circuit diagram of one portion of the block diagramof FIG. 9;

FIG. 11 is a schematic circuit diagram of a portion of the block diagramof FIG. 10;

FIG. 12 is a schematic circuit diagram of another portion of the blockdiagram of FIG. 10;

FIG. 13 is a schematic circuit diagram of a portion of the block diagramof FIG. 9;

FIG. 14 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 9;

FIG. 15 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 9;

FIG. 16 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 9;

FIG. 17 is a schematic circuit diagram of another portion of theembodiment of the motor control circuit of FIG. 2;

FIG. 18 is a block diagram of still another portion of the block diagramof FIG. 2;

FIG. 19 is a block diagram of another portion of the block diagram ofFIG. 2;

FIG. 20 is a block diagram of a portion of the block diagram of FIG. 18;

FIG. 21 is a schematic circuit diagram of another portion of the blockdiagram of FIG. 18;

FIG. 22 is a block diagram of a portion of the block diagram of FIG. 20;

FIG. 23 is a schematic circuit diagram of a portion of the block diagramof FIG. 22;

FIG. 24 is a schematic circuit diagram of another portion of the blockdiagram of FIG. 22;

FIG. 25 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 20;

FIG. 26 is a block diagram of still another portion of the block diagramof FIG. 2;

FIG. 27 is a block diagram of still another portion of the block diagramof the motor control system of FIG. 2;

FIG. 28 is a schematic circuit diagram of a portion of the block diagramof FIG. 26;

FIG. 29 is a schematic circuit diagram of still another portion of theblock diagram of FIG. 26;

FIG. 30 is a sectional view, partly schematic, of a pump in accordancewith an embodiment of the invention; and

FIG. 31 is a schematic circuit diagram of an average rate of flowcircuit.

DETAILED DESCRIPTION

In FIG. 1, there is shown a block diagram of a chromatographic system10, having a low pressure system 12, a high pressure pumping system 14,a high pressure pump control system 16, a chromatographic column, aninjector system 18 and a detector and collector system 20. The highpressure pumping system 14 communicates with the low pressure system 12to receive solvents therefrom and with the chromatographic column andinjector 18 to supply the influent thereto for detection and at timescollection by the detector and collector system 20.

To control the high pressure pumping system 14, the high pressure pumpcontrol system 16 is electrically connected to the low pressure system12 from which it receives signals relating to the flow rate of theinfluent to the chromatographic column and injector system 18 and iselectrically connected to the high pressure pumping system 14 tomaintain that flow rate as constant as possible.

The low pressure system 12, the chromatographic column and injectorsystem 18 and the detector and collector system 20 are not part of thisinvention except insofar as they cooperate with the high pressurepumping system 14 and the high pressure pump control system 16 toprovide a constant flow rate of solvents through the chromatographiccolumn and injector system 18.

The low pressure system 12 includes a low pressure pumping and mixingsystem 24 and a general system controller 22. The general systemcontroller 22 contains flow rate information and, in someconfigurations, gradient information as well as information forinjecting samples into the chromatographic column or providing dataacquisition and processing functions in conjunction with the detectorand collector system 20. The general system controller 22 is not part ofthe invention except insofar as it provides signals to the high pressurepump control system 16 to control the flow rate from the high pressurepumping system 14.

In FIG. 2, there is shown a block diagram of the high pressure controlsystem 16 having a motor circuit 30, a flow rate circuit 32, a firstflow rate control system 34, a second flow rate control system 36 and anaverage flow rate control loop circuit 47. The first flow rate controlsystem and the second flow rate control system each apply signals to theflow rate control circuit through conductors 62 and 64, one of themapplying generally linear signals during at least a portion of eachcycle of operation of the motor circuit and the other applying nonlinearsignals through conductor 64.

The linear and nonlinear signals control a pulse-width-modulator withinthe flow rate circuit 32 which ultimately controls the speed of themotor circuit 30 to maintain the flow rate of the fluid through thechromatographic column and injector system 18 (FIG. 1) as nearlyconstant as possible. The linear and nonlinear signals are related, withthe nonlinear signal being larger or smaller in relation to the linearsignal and for this purpose the first flow rate control system andsecond flow rate control system are electrically connected through aconductor 556 in a manner to be described hereinafter. The average flowrate control loop circuit periodically measures output liquid flowduring each cycle of the pump and changes the signal on conductor 46representing the preset flow rate to maintain an average flow rate equalto the preset flow rate.

To provide a substantially linear signal during at least a portion ofthe motor circuit 30, the first flow rate control system 34 includes alinear flow rate control circuit 38 and a first compensation circuit 40.The first compensation circuit 40 receives signals from the motorcircuit 30 to provide certain correction signals to the linear flow ratecontrol circuit 38 to which it is connected. The linear flow ratecontrol circuit 38 receives signals from the system controller 22(FIG. 1) on a conductor 46 indicating the desired rate of flow andsupplies a resulting signal to the flow rate circuit 32 which includescorrections made in response to the motor circuit 30 and from the firstcompensation circuit 40.

To provide a signal to the flow rate control circuit 32 to acceleratethe pump motor, the nonlinear flow rate control system 36 includes anonlinear flow rate control circuit 42 and a second and positivefeedback compensation circuit 44 (hereinafter second compensationcircuit). The nonlinear flow rate control circuit 42 receives signalsfrom the motor circuit 30 to which it is electrically connected andapplies signals through an electrical connection to the flow ratecircuit 32 as modified by signals from the second compensation circuit44.

With this arrangement, the high pressure pump control system 16maintains the flow rate through the column relatively constant at theprogrammed rate to cause the time at which peaks are detected to bereproducible because of pulses of fluid of different rates occurring atdifferent times in the column rather than constantly eluting themolecular species from the column. Generally, the high pressure pumpcontrol system 16 controls the pump motor through the motor circuit 30in such a way as to maintain the average flow of fluid at the presetrate and to minimize rapid fluctuations in flow rate such as might becaused by a refill stroke of a piston pump or the like.

In FIG. 3, there is shown a block diagram of the flow rate circuit 32and the motor circuit 30. The flow rate control circuit 32: (1) receivesa signal on conductor 62 during a portion of a pump cycle which is theoutput of a servo loop and has a substantially linear relationship withthe desired pumping rate; and (2) a signal on conductor 64 which is aramp nonlinearly corrected in slope to relate to the preset average flowrate, to the accelerating refill speed. Both signals contain somecorrections which are directed to establishing a rate of pumping whichpermits a single piston reciprocating pump to approach constant flowthrough a chromatographic column across a period of time.

The flow control circuit 32 is electrically connected to the motorcircuit 30 through a conductor 66 to apply to the motor circuit 30periodic pulse-width-modulated signals in which the pulse width (dutycycle) is related to the speed at which the piston is intended to moveto: (1) reduce flow rate pulsations in the chromatographic column bymaintaining the average rate of flow of influent to the column in asconstant as possible; and (2) changing the piston speed to reduce thetime that the pump is not forcing fluid through its outlet port. Thespeed of the piston is controlled to avoid cavitation or changes in theflow rate that are so sudden as to disrupt the rate of flow through thechromatographic column and injector system 18 (FIG. 1).

To provide a speed of piston movement for constant flow rate of theinfluent to the chromatographic column and detector system 18 (FIG. 1),the motor circuit 30 includes a motor 50, a brake circuit 52, a refillinception detector circuit 54, a tachometer disc and sensors system 58,and an overcurrent sensor circuit 60. The motor 50 is driven by powerapplied through the conductor 66 from the flow rate control circuit 32and drives the piston of the pump (not shown in FIG. 3) through itsoutlet shaft 56.

To slow the pump, dynamic braking is under some circumstances applied tothe motor through the brake circuit 52 in response to control signals ona conductor 70 indicating the time of application of the braking. Thebrake circuit 52 transmits signals through a conductor 72 to the firstcompensation circuit 40 (FIG. 2) which is used to adjust the motor speedat the end of a motor acceleration portion of a cycle to reduce drivepower to the motor.

To aid in coordinating the pump motor control circuit within the secondcompensation circuit 44 (FIG. 2) the refill inception detector circuit54 transmits a signal on conductor 76 for application to the firstcompensation circuit 40 (FIG. 2) at the end of a liquid delivery stroketo initiate a refill portion of a cycle. This signal aids in timing thestart and termination of motor acceleration.

To generate signals indicating the volume of fluid pumped and motorspeed, the tachometer disc and sensors system 58 generates signals forapplication through conductor 78 to the linear flow rate control circuit38 (FIG. 2) and the average flow rate control loop circuit 47 (FIG. 2).The overcurrent sensor circuit 60 detects currents which exceed a presetvalue in the motor circuit, usually indicating binding or a bearingfault, so as to avoid damage to of the pump.

In FIG. 4, there is shown a schematic circuit diagram of the flow ratecontrol circuit 32 having a comparator circuit shown generally at 80 anda drive circuit shown generally at 82, with the comparator circuit 80receiving a ramp signal on conductor 64 from the second flow ratecontrol system 36 (FIG. 2), a linear signal on conductor 62 from thefirst flow rate control circuit 34 (FIG. 2) and an over-currentprotection signal on conductor 84 from the second flow rate controlsystem 36 (FIG. 2).

These signals result in a positive-going variable width 13 KHz(kilohertz) pulse train being applied by the comparator through aconductor to the driver circuit 82 inversely related to how steep theramp circuit applied to conductor 64 is, directly related to theamplitude of the signal applied to 62, which determines the duty factorof the pulse train.

The motor driver circuit 82, during the time duration it receives thepulse train from the comparator 80, applies a variable voltage acrossconductors 66A and 66B, resulting in power being applied to the motor 50(FIG. 3) during a time controlled by the pulse-width-modulator 32 andconsistent with the pulse train applied by the comparator 80.

To compare the ramp signal on conductor 64 with the servo input signalon conductor 62, the comparator circuit 80, is a LM 311 voltagecomparator sold by National Semiconductor, 2900 Semiconductor Drive,Santa Clara, Calif. 25051, and described in its 1985 catalogue "LinearIntegrated Circuits", having pin 1 electrically connected to the drivercircuit 82, pin 2 electrically connected to conductor 62 through a 10 Kresistor 92 to receive the servo input signal, pin 3 electricallyconnected to conductor 64 to receive the ramp, pin 4 electricallyconnected to a source 94 of a negative 12 volts and to the electricalcommon through a 1 uf (microfarad) capacitor 96, pin 6 electricallyconnected to conductor 84 to receive an overcurrent signal from thesecond flow rate control system 36 (FIG. 2) and pin 8 electricallyconnected to a source 98 of a positive 12 volts. An equivalent circuitwould be a simple comparator having an inverter on its output connectedto one input of a two input AND gate and conductor 84 connected to theother input.

The comparator 86 has its noninverting input terminal electricallyconnected to conductor 62 through the resistor 92 and its invertinginput terminal electrically connected to conductor 64. A first rail iselectrically connected to the source 94 of a minus 12 volts and toelectrical common through the capacitor 96 and its other railelectrically connected to the source 98 of a positive 12 volts. Theoutput of the comparator from pin 1 is electrically connected to thedrive circuit 82 to apply a signal thereto corresponding to the time inwhich the ramp voltage applied on conductor 64 is less than the level onconductor 62.

The drive circuit 82, includes a MTP12NO5 MOSFET transistor 102, aMR2400F diode 104 (all manufactured by Motorola Corporation), and asource 106 of a positive 32 volts. The gate of the transistor 102 iselectrically connected: (1) to the output of the comparator 86 through a33 ohm resistor 108; (2) to a source 112 of a negative 8 volts through a820 ohm resistor 110; (3) to the overcurrent sensor circuit 60 (FIG. 3)through the reverse resistance of a 1N5245B Zener diode 114; and (4) toa source 98 of a positive 12 volts through the resistor 110.

The source of the transistor 102 is electrically connected to theovercurrent sensor circuit 60 (FIG. 3) through a conductor 118. Toprovide noise filtering for the comparator 86, the source 98 of apositive 12 volts is electrically connected to electrical common throughtwo 1 uf capacitors 120 and 122 in parallel with each other and to thesource 112 of a negative 8 volts through a 1 uf capacitor 116, with asource of negative volts 112 also being electrically connected to thegate through the resistor 110 to provide biasing directly to the gate. A0.2 uf capacitor 174 is connected across conductors 66A and 66B tofilter lower frequencies.

Conductor 118 is essentially grounded for power supply purposes and thedrain is electrically connected through the forward resistance of thediode 104 to the source 106 of a positive 32 volts and to conductor 66Aso that, the positive 32 volts is connected at all times to one end ofthe armature of the motor 50 (FIG. 3), conductor 66B on the otherarmature and being electrically connected through a current limitinginductor 124 to the anode of the diode 104 and the drain of thetransistor 102. The capacitance across the motor is essentially 2 uf.The motor is a Pitman 13000 series DC motor and the inductor issubstantially 200 uh (microhenries).

With this circuit arrangement, when the transistor 102 is condeucting asa result of the positive pulse at its gate, current flows from thesource 106 of a positive 6 volts through the motor, the inductor 124 andthe traqnsistor 102 to ground through conductor 118, and when thepositive pulse is not applied, the current is maintained by inductor 124through diode 104 and, the motor and back through the inductor unlessthe motor is operating to generate current for dissipation in the brakecircuit 52 (FIG. 3) to be described hereinafter.

With this arrangement, when the linear feedback circuit indicates thatthe motor speed falls below its preset speed, the pulse width isincreased linearly and when the nonlinear feedback circuit indicates theneed for acceleration to equalize the flow, the width of the pulse isincreased provide a correction of motor speed in a velocity feedbackloop during a portion of a pump cycle prior to refill. The nonlinearfeedback circuit provides an acceleration signal prior to the constantflow portion of the delivery for a longer time as the flow rate duringthe last portion of delivery increases and a shorter time as itdecreases.

In FIG. 5, there is shown a schematic circuit diagram of the brakecircuit 52 (FIG. 3) having an input logic circuit 130, a drive circuit132, and a shunt circuit 134. The input logic circuit receives a signalon conductor 70 from the second flow rate correction circuit 36 (FIG. 2)and causes the drive circuit 132 to form a conducting path in the shuntcircuit 134 across the armature of the motor to provide dynamic braking.The input logic circuit also applies output signals through conductor 72to the second flow rate compensation circuit (FIG. 2) and to conductor62 to the flow rate control circuit 32 (FIG. 3).

To provide a signal causing dynamic braking, the input logic circuit 130includes a NAND gate 136, input conductor 70 and output conductors 72and 62. The NAND gate 136 has one of its inputs electrically connectedto a source 138 of a positive 8 volts and its other input electricallyconnected to the input 70 through a 10 K resistor 140 to receive signalsfrom the second flow rate correction system 36 (FIG. 2) indicating abraking action. The output of the NAND gate 136 is electricallyconnected to conductor 72 to provide a positive output signal whenbraking action is to occur and to conductor 62 through the 1N5060 diode142 to turn off drive pulses from the flow rate control circuit 32.

To energize the dynamic brake, the drive circuit 132 includes first andsecond NPN transistors 150 and 152 and a diode 154. The anode of thediode 154 is electrically connected to the output of the NAND gate 136and its cathode is electrically connected to the base of the transistor150 through a 4.7 K (kilohm) resistor 156 and to electrical commonthrough a 4.7 K resistor 158. The emitter of transistor 150 iselectrically connected to the base of transistor 152 and to electricalcommon through a 470 ohm resistor 160 and the emitter of transistor 152is directly connected to electrical common. The collector of thetransistors 150 and 152 are each electrically connected to the input tothe shunt circuit 134 through two 39 ohm resistors 162 and 164electrically connected in series. The transistors 150 and 152 are 2N3704and D44C8 transistors manufactured by G.E. Corporation and described inthe catalogue and the diode 154 is a type 1N914 diode.

To form a conducting path for current generated by the pump motor whenit is being driven by inertia and thus to provide dynamic braking theshunt circuit 134 includes a D45H8 PNP transistor 170, and a 1N5060diode 172. The transistor 170 has its base electrically connected to theoutput of the drive circuit 132, its emitter electrically connected toits base through a 220 ohm pull-down resistor 173 and its collectorelectrically connected through the diode 172 to its emitter and toconductor 74B through a resistor 176.

The emitter of the transistor 170 is electrically connected to conductor66A so that, when the motor operates as a generator for dynamic braking,a path is formed between conductors 66A and 66B through the motor andtransistor 170 when transistor 170 is saturated and provides an opencircuit when the motor is driven as a motor.

In FIG. 6, there is shown a schematic circuit diagram of the refillinception detection circuit 54 (FIG. 3), having an optical sensor 180, arotatable flag 182 on the cam shaft, and a comparator 184. The flag 182shown in fragmentary schematic form, rotates with the cam shaft on it ina location to be detected by the optical sensor 180, which transmits apositive going pulse in response to a signal indicating the start of therefill cycle to the noninverting input terminal of the comparator 184.The comparator 184 signals the second flow rate control system 36 (FIG.2) indicating the start of the refill cycle in response to the detectedsignal.

For this purpose, the comparator 184 has its noninverting input terminalelectrically connected to electrical common through a 2.2 K resistor 186and to the output of the optical sensor 180. The inverting inputterminal of the comparator 184 is electrically connected to conductor76B, to electrical common through a 100 ohm resistor 188 and to a source112 of a negative 8 volts through a 1.5 K resistor 190 so that areference potential is established, above which a signal is providedthrough conductor 76A indicating a refill cycle. The comparator 184 haspositive and negative 8 volt rails at 138 and 112.

The optical sensor 180 has a light emitting diode, with its anodeelectrically connected to electrical common and its cathode electricallyconnected to a source of negative 8 volts through a 1.5 K resistor 192and has a light sensitive transistor therein with its collectorelectrically connected to the noninverting input terminal of thecomparator 184 and its NPN emitter junction electrically connected tothe source 112 of a negative 8 volts.

In FIG. 7, there is shown a schematic circuit diagram of the overcurrentsensor circuit 60 (FIG. 3) having a current sensing network 202, areference network 204 and a comparator circuit 206 The sensing network202 senses the motor current and the reference network 204 provides partof the reference with both values being compared in the comparatorcircuit 206 to provide an output signal disabling the average flow ratecontrol circuit 32 (FIG. 3 and FIG. 4) when the motor current is toohigh indicating a jammed condition of the pump or the like.

To sense the current through the pump, the current sensing network 202includes three 0.1 ohm resistors 210, 212, and 214 respectivelyconnected in parallel between a conductor 216 and a conductor 218.Conductor 216 is electrically connected to conductor 118 to receivemotor current and conductor 218 is electrically connected to theelectrical common so that the current flow through the motor onconductor 118 causes a voltage drop in the sensing network 202, whichvoltage drop occurs between conductors 216 and 218.

To provide a reference potential, the reference network 204 iselectrically connected: (1) through 86.6 K resistor 240 to 4.7 Kresistor 234 and thence to the source of a positive 8 volts; (2) toconductors 216 and 218; and (3) to the comparator circuit 206 throughconductors 220 and 222. Conductor 216 is electrically connected througha conductor 200 to the anode of the Zener diode 114 (FIG. 4) of the flowrate control circuit 32 (FIGS. 2, 3 and 4) to receive currenttherethrough and to conductor 220 through a 1 K resistor 224. Conductor218 is electrically connected to conductor 222 through a 4.75 K resistor226 and to a source 112 of a negative 8 volts potential through a 309 Kresistor 228.

With this arrangement, conductor 222 is maintained at a potential abovethe electrical common by the sources of potential 138 and resistors 234and 240.

To compare the potential on conductors 220 and 222 for the purpose ofindicating an overcurrent, the comparator circuit 206 includes thecomparator 230 which is manufactured and sold by National SemiconductorCorporation (2900 Semiconductor Drive, Santa Clara, Calif. 95051) type311 having its inverting input terminal at pin 3 electrically connectedto conductor 220 and its noninverting input terminal at pin 2electrically connected to conductor 222 to provide a comparison of thevoltages therein.

During an overcurrent, the output at pin 7 of the comparator goes from 8to common potential. The removes positive potential from resistor 240and negative potential from sources 112 through resistor 278 causes thecomparator to latch up and disable the motor drive circuit.

At the end of the pulse cycle, a reset pulse on pin 6 at 296 resets thecomparator from a clock in the second positive feedback and compensationcircuit 44 to enable the comparator and motor drive circuit 32.

The output of the comparator 230 at pin 7 is electrically connected to:(1) the source 138 through the resistor 234, (2) a conductor 84 through680 ohm resistor 239; (3) the reverse resistance of the 8.2 IN5237 voltZener diode 237 and the foreward resistance of diode 238; and (4)conductor 222 through a 86.6 K resistor 240. The conductor 84 (FIG. 4)is electrically connected to the pulse-width-modulator 86 (FIG. 4) sothat conductor 84 provides signals to disable the flow rate circuit 32(FIGS. 2, 3 and 4) by de-energizing the comparator 86 upon a currentoverload condition.

In FIG. 8, there is shown a schematic circuit diagram of the tachometerdisc and sensor system 58 (FIG. 3) having a first and a second opticalsensor 250 and 252 respectively, rotatable disc 254 and first and second270 ohm resistors 258 and 260 respectively. The first and second opticalsensors sense indicia indicating the rotation of the pump on disc 254which is mounted to the output shaft of the pump motor. The opticalsensors 250 and 252 are located in quadrature with respect to theindicia so as to indicate the amount of rotation of the motor and itsdirection in a manner in the art.

With this arrangement, the optical sensors provide signals indicatingthe amount of rotation and direction of the motor by rotation of thedisc in one direction as well as position of the piston in part of adelivery stroke by sensing indicia at equispaced distances along thedisc 254. This type of circuit is described in U.S. co-pendingapplication Ser. No. 713,328 to Robert W. Allington, et al, assigned tothe same assignee as this application and filed Mar. 18, 1985.

To sense indicia on disc 254 the first optical sensor 250 includes alight emitting diode having its anode electrically connected to theelectrical common and its cathode electrically connected to the source112 of a negative 8 volts through the resistor 258. To provideelectrical signals indicating the amount of electrical rotation of thedisc 254, the first optical sensor 250 includes a light sensitiveelement separated from the light emitting diode by the disc 254 to havelight blocked or transmitted to it as the disc 254 rotates.

The light sensitive element has its collector electrically connected tothe linear flow rate control circuit 38 (FIG. 2) and nonlinear flow ratecontrol circuit 42 (FIG. 2) and average flow rate control loop circuit47 (FIG. 2) through a conductor 262 and has its emitter electricallyconnected to the source 112 of a negative 8 volts to provide electricalsignals to conductor 262 indicating the amount of rotation of the pump.

The second light sensor 252 has a light emitting diode in it with itsanode electrically connected to the electrical common and its cathodeelectrically connected to the source 112 of a negative 8 volts throughthe 270 ohm resistor 260. It has a light sensitive element separatedfrom the light emitting diode 252 by the rotatable disc 254 so as tosense indicia upon it.

The light sensitive element has its collector electrically connected tothe linear and nonlinear flow rate control circuit 38 and 42 (FIG. 2)through a conductor 264 and average flow rate control loop circuit 47(FIG. 2) and has its emitter electrically connected to the source 112 ofa negative 8 volts so as to provide electrical signals to conductor 264indicating the amount of rotation of the disc 254 with the signals onconductors 262 and 264 indicating the amount of rotation and thedirection of rotation.

In FIG. 9, there is shown a block diagram of the nonlinear flow ratecontrol circuit 42 (FIG. 2) having a quadrature detector 270, afrequency to voltage converter 272, a multivibrator circuit 274, anexponential amplifier circuit 276 and a ramp generator 278. Thequadrature detector 270 is electrically connected to conductors 262 and264 to receive signals from the tachometer disc and sensor system 58(FIGS. 3 & 8) and apply a signal indicating the amount of rotation inone direction to a conductor 290 to the frequency to voltage converter272 which generates a signal representing in amplitude the rate ofrotation of the motor for application to a conductor 280.

Conductor 280 is electrically connected to the exponential amplifiercircuit 276 and the output from the exponential amplifier circuit 276and from the multivibrator circuit 274 are connected to the rampgenerator 278 to generate a ramp which varies in slope in a mannerrelated to the motor speed.

To receive correcting signals, the second compensation circuit 44 (FIG.2) is connected to the ramp generator 278 through a conductor 282 and toselect the flow rate operating range of the frequency to voltageconverter control signal is applied to the frequency to voltageconverter 272 from the linear flow rate control circuit 38 (FIG. througha conductor 284 to select a flow rate range.

In FIG. 10, there is shown a block diagram of the quadrature detector270 (FIG. 9) having a pulse output conductor 290, a direction circuit292 and a tachometer sensor input circuit 294. The tachometer sensorinput circuit 294 is electrically connected to conductors 262 and 264 toreceive signals from the first and second optical sensors 250 and 252(FIG. 8) respectively, which sensors generate pulses at the samefrequency as the motor rotates but 90 degrees out of phase. The outputof the tachometer sensor input circuit 294 applies both sets of pulsesto the direction circuit 292 which selects only those pulses whichindicate a forward movement of the pump piston or plunger forapplication to the output at conductor 290. This circuit is explained inthe aforementioned patent application.

The tachometer sensor input circuit 294 includes a first channel 296 anda second channel 298 with the first channel 296 being electricallyconnected to the first optical sensor 250 through conductor 262 toreceive signals therefrom and electrically connected to the directioncircuit 292 through a conductor 300 and the second channel 298 beingelectrically connected to the second sensor 252 (FIG. 8) through theconductor 264 to receive signals therefrom and to the direction circuit292 through a conductor 302 to supply signals thereto. The first channel296 is identical to the first channel 298 except that they receivesignals from different sources and supply to the direction circuit 292through different conductors.

In FIG. 11, there is shown a schematic circuit diagram of the firstchannel 296 (FIG. 10) within the tachometer sensor input circuit 294(FIG. 10) having a first operational amplifier 304 and a secondoperational amplifier 306. The amplifiers 304 and 306 are type LM353amplifiers each having one rail connected to a source 138 of a positive8 volts and the other rail electrically connected to a source 112 of anegative 8 volts.

To provide amplification and low pass noise filtering, amplifier 304 hasits noninverting input terminal electrically connected to the electricalcommon and its inverting input terminal electrically connected to: (1)conductor 262 through a 470 ohm resistor 308 and to a source 138 of apositive 8 volts through the resistor 308, a 27 K resistor 310 and avariable 50 K resistor 312 so as to permit adjustment of the input tooperating current of the light sensor connected to conductor 262. Theoutput of amplifier 304 is electrically connected to: (1) its invertinginput terminal through a 56 K resistor 314 and a 150 pf (picofarad)capacitor 316 electrically connected in parallel; and (2) to thenoninverting input terminal of the amplifier 304 through a 47 K resistor318.

To provide Schmidt Tragger action, amplifier 306 has its outputelectrically connected to: (1) conductor 300 through a 4.7 K resistor320, a source 138 of a positive 8 volts through the resistor 320 and theforward resistance of a 1N273 diode 322; (3) and the electrical commonthrough the reverse resistance of a 1N273 diode 324; (4) to itsnoninverting input terminal through a 1.2M resistor 326 and to theelectrical common through the resistor 326 and a 47 K resistor 328.

In FIG. 12, there is shown a schematic circuit diagram of the directioncircuit 292 (FIG. 10) having a divide-by-two circuit 330, an up-downcounter circuit 332 and an input gating circuit 334. The gating circuit334 is electrically connected to conductors 300 and 302 to receivesignals processed by channels 1 and 2 from the first and second sensors250 and 252 respectively (FIG. 8) and has its output electricallyconnected to the up-down counter circuit 332 which caused by backwardmovement of counts pulses proportional the motor, by counting backwardsfrom 15 and requiring recounting of those pulses in the forwarddirection for application to the divide-by-two circuit 330 andeventually to output conductor 290 to the frequency to voltage converter272 (FIG. 9).

The input gating circuit 334 includes four exclusive OR gates 336, 338,340, and 342 and one NOR gate 344. Conductor 300 is electricallyconnected to one input of each of the exclusive 0R gates 338 and 342 andconductor 302 is electrically connected to another input of the twoinput exclusive OR gates 338 and 342 and to: (1) an input of theexclusive OR gate 342 through a 150 K resistor 346; and (2) to theelectrical common through the resistor 346 and a 120 pf capacitor 348.The output of exclusive OR gate 338 is electrically connected to: (1)one of the two inputs of the exclusive OR gate 336; (2) the input of theNOR gate 344 through a 27 K resistor 350; and (3) the electrical commonthrough the resistor 350 and a 120 pf capacitor 352.

The output of the exclusive OR gate 342 is electrically connected to oneof the two inputs of the exclusive OR gate 340, the other input beingelectrically connected to a source 138 of a positive 8 volts. The outputof the exclusive OR gate 336 is electrically connected to the up-downcounter circuit 332 through a conductor 354 and the output of the ORgate 340 is electrically connected to the up-down counter circuit 332through a conductor 356 to provide signals corresponding to the firstand second sensor thereto modified so that signals received from thefirst sensor before the second count up and signals received by thesecond sensor before the first sensor count down.

The up-down counter circuit 332 includes a type 4029 up-down counter 360and a type 4002B NOR gate 362. Conductor 354 is electrically connectedto pin 15 of the counter 360 to cause it to count up and conductor 356is electrically connected to pin 10 of the counter 360 to cause it tocount down and to one of the four inputs of the NOR gate 362, the outputof which is electrically connected to pin 5 to inhibit counting uponreceiving a signal on conductor 356 passing through the NOR gate 362.

Pins 2, 14, and 11 of the counter 360 are each electrically connectedto: (1) a different one of the other three inputs of the NOR gate 362;and (2) a different one of the 10 K resistor 364, 22 K resistor 366 and39 K resistor 368. The other end of the resistors 364, 366, and 368 areeach electrically connected to: (1) pin 6 of the counter 60 through an82 K resistor 370; and (2) the electrical common through a 1 K resistor372. Pins 8 and 4 of the counter 360 are grounded and pins 16, 13, 12, 9and 3 are electrically connected to the source 138 of a positive 8 voltsto determine the output voltage of the counter. Pins 1 and 7 areelectrically connected to conductors 374 and 376 to provide outputpositive 8 volt pulses as the counter counts in binary notation upwardlyin response only to signals caused by rotation of the motor in thedirection which enables the piston to force fluid from the cylinder ofthe pump. The counter counts downwardly in response to reverse rotationbut is inhibited from counting past zero.

To divide the binary signals applied on conductors 374 and 376 in two,the divide-by-two circuit 330 includes a type 4013B divider 374 havingpins 3 and 11 electrically connected to conductor 376 and pin 13: (1)electrically connected to conductor 374 and to pin 10 through a 2.7 Kresistor 380; and (2) to the electrical common through resistor 380 anda 0.01 uf capacitor 382. Pins 9 and 14 of the divider 378 are eachelectrically connected to the source 138 of a positive 8 volts, pin 1 iselectrically connected to conductor 290 to provide a frequency outputrepresenting the rate of flow of effluent from the pump, pins 2 and 5are electrically connected together and pins 4, 6, 8 and 7 are eachelectrically connected to the electrical common.

In FIG. 13, there is shown a schematic circuit diagram of a frequency tovoltage converter 272 (FIG. 9) having an analog switch 390, an LM2907frequency to voltage converter 392 and a gain adjustment circuit 394.

The frequency to voltage converter may be any suitable type, many ofwhich are known in the art but in the preferred embodiment it is anintegrated circuit sold by National Semiconductor under the designationLM2907. Pin 1 of that unit is electrically connected to conductor 290 toreceive pulses from the tachometer disc and sensor system 58 (FIGS. 3 &8) through a 22 K resistor 396. This circuit is part of a tachometerthat produces an output voltage proportional to motor speed.

The conductor 290 is also electrically connected to the electricalcommon through the resistor 396 and a 22 K resistor 398 and to thesystem controller 22 (FIG. 1) through a 10 K resistor 402 and aconductor 400 where it may be used by the system to indicate theprogress of the chromatographic run. The frequency to voltage converter392 has pin 11 electrically connected: (1) through a source 138 of apositive 8 volts and 47 K resistor 404 for biasing; and (2) through a0.47 uf capacitor 406 and a 15 K resistor 408 to the electrical commonin parallel to short out noise. Pins 7 and 12 are electrically connectedto a source 112 of a negative 8 volts and to the electrical commonthrough a 1 uf capacitor 410, pins 8 and 9 electrically connected to asource 138 of a positive 8 volts and to the electrical common through a1 uf capacitor 412.

To accommodate changes in pumping speed frequency to voltage converter392 has pin 2 electrically connected to: (1) the electrical commonthrough an 820 pf capacitor 414; and (2) one lead of 4016 analog switch390 through an 820 pf capacitor 416. The gate of the analog switch 390is connected to conductor 418 to receive a low range signal and theother level is electrically connected to the electrical common through a33 K resistor 422.

The switch 390 doubles the gain of the frequency to voltage converter bydoubling capacitance by switching capacitor 416 in parallel with 414 toprovide low range operation at a high scale with an addition multiplierto be described hereinafter upon receiving a signal on conductor 418.

To control the gain of the voltage conversion provided by frequency tovoltage converter 392, the gain control circuit 394 includes a first 5 Kpotentiometer 424 and a second 5 K potentiometer 426 with thepotentiometer 426 being connected at one end to a source 138 of apositive 8 volts and at the other end to a source 112 of a negative 8volts, its variable tap being electrically connected through a 10megaohm resistor 427 to: (1) pin 10 through a switch which may be openedor closed; (2) and pin 3 of the frequency to voltage converter 392; (3)pin 5 through a 0.022 uf capacitor 428 and a 0.33 uf capacitor 430; and(4) to the tap of the potentiometer 424 through a 30.9 K resistor 432.

The potentiometer 424 is electrically connected at one end to aconductor 280 and to pin 5 of the frequency to voltage converter 392 andat its other end to the electrical common through a 10 K resistor 436and directly to pin 5 of the frequency to voltage converter and to pin 5of the voltage to frequency converter through the capacitor 430.Conductor 280 applies the voltage corresponding to the rate of flow offluid to the exponential amplifier circuit 276 (FIG. 9) throughconductor 280 and to the first compensation circuit 40 (FIG. 2).Conductor 280 is electrically connected to the source 94 of a negative12 volts through a 604 ohm resistor 440.

With this arrangement, the amplitude of the voltage output may beadjusted by potentiometer 424 and 426 to provide a voltage which variesin relation to the rate of flow of fluid as measured by the tachometer.This voltage is applied to the first compensation circuit 40 (FIG. 2)for application to the linear flow rate control circuit 38 (FIG. 2) andto the exponential amplifier circuit 276 (FIG. 9) through conductor 280to control the nonlinear flow control circuit 42 (FIG. 2).

In FIG. 14, there is shown a schematic circuit diagram of themultivibrator circuit 274 (FIG. 9) having a conventional astablemultivibrator 450 which may be of any conventional designation but inthe preferred embodiment is a National Semiconductor 55 multivibratorconnected as shown to provide a suitable frequency during a portion ofthe time normally required for a full piston stroke of the pump. Thefunction of the multivibrator circuit is to reset the overload circuitand the ramp generator.

To provide the proper frequency, the multivibrator circuit 274 includes:(1) 3 capacitors 452, 454, and 456 having values of 1 uf, 0.01 uf and2200 pf respectively; (2) 2 resistors 458 and 460 having values of 680ohms and 39.2 ohms respectively; and (3) a 10 K potentiometer 462 withpins 4 and 6 of the multivibrator 450 being electrically connected toone end of the potentiometer 462, pin 7 being electrically connected to:(1) to the other end of the potentiometer 462 through the resistor 460;(2) to pins 6 and 2 of the multivibrator 450 through the resistor 458;and (3) to the electrical common through the capacitor 456. Theelectrical common is also electrically connected to pin 1, to pin 5through the capacitor 454 and to pins 4 and 8 through the capacitor 452.

To provide a reset pulse to the ramp generator 278 (FIG. 9) and to theflow rate control circuit 32 (FIGS. 2, 3 & 4) pin 3, which is the outputof the multivibrator 450, is electrically connected to conductor 470 toapply a positive pulse thereto for initiating a ramp circuit andproviding an output pulse from the flow rate control circuit 32 (FIGS.2, 3 & 4) through conductor 84. To provide a signal to the ramp circuitto initiate a ramp, the multivibrator 274 includes a source 112 of anegative 8 volts electrically connected to conductor 470 through a 3.9 Kresistor 472 and a 1.82 K resistor 474 with output conductor 476 beingelectrically connected to resistor 472 and 474 to change from a negativeto a positive value upon receiving a signal from the multivibrator 450.Conductor 476 is electrically connected to the ramp generator 278 (FIG.9).

To provide a turn-off signal on conductor 84 to the flow rate controlcircuit 32 (FIGS. 2, 3 & 4) conductor 84 is electrically connected toconductor 470 through a 680 ohm resistor 478, the reverse resistance ofCR106 zener diode 480 and the forward resistance of a 1N914 diode 482.

To reset the overcurrent sensor 60 (FIGS. 3 & 7), conductor 296 to theovercurrent sensor 60 is electrically connected through a 680 ohmresistor 484 and through the forward resistance of a 1N914 diode 486 toconductor 470 to apply a positive potential thereto, permitting the flowrate control circuit 32 (FIGS. 2, 3 & 4) to operate.

In FIG. 15, there is shown a schematic circuit diagram of theexponential amplifier circuit 276 (FIG. 9) having a first PNP 2N3702transistor 490, a second PNP 2N4061 transistor 492, an adjustmentcircuit 496 and a bias circuit 494. The transistor 490 has a lower inputimpedance than and conducts approximately ten times the current throughtransistor 492 causing transistor 492 to follow the potential onconductor 280, thus providing an exponential drop between the emitterand base of trransistor 492. The two transistors cancel theirtemperature coefficients. The first transistor 490 receives an inputsignal from the frequency to voltage converter 272 (FIGS. 9 & 13) onconductor 280 indicating the speed of pumping and varies the emitterbias of the transistor 492 to cause an exponential amplification of thesignal from the frequency to voltage converter 272 for applicationthrough a conductor to the ramp generator circuit 278 (FIG. 9).

To provide emitter biasing to the first and second transistors 490 and492, the emitters of each of these transistors is electrically connectedto a source 98 of a positive 12 volts through a 1.18 K resistor 502 andto a second such source through the 1.18 K resistor 502 and a 33 ohmresistor 500.

To vary the emitter potential of the second transistor 490 in a mannerrelated to the input amplitude on conductor 280 from the frequency tovoltage converter 272 (FIGS. 9 & 13) so as to provide an exponentialtransfer function, the base of the transistor 490 is electricallyconnected to: (1) the electrical common through a 47.5 ohm resistor 508;(2) to input conductor 280 through a 1.40 K resistor 504; and (3) to asource 106 of a positive 32 volts through a 45.3 K resistor 506. Thecollector of the transistor 490 is electrically connected to a source112 of a negative 8 volts so that it will draw current through theemitter biasing circuit from the source 98 of a positive 12 volts andthrough the resistor 502 in proportion to the input signal on conductor280 and thus cause a drop in the positive potential on the emitter ofthe transistor 492 as the current increases.

To provide a further adjustment on a sawtooth waveform to be controlledby the transistors 490 and 492, the adjustment circuit 496 includes a1.18 K resistor 510, a 100 K resistor 512 and a 5 K potentiometer 514.To establish biasing, one end of the potentiometer 514 is electricallyconnected to a source 138 of a positive 8 volts and the other end iselectrically connected to a source 112 of a negative 8 volts, with themovable tap being electrically connected to the base of the transistor492 through a 100 K resistor 512. The base of the transistor 492 is alsoelectrically connected to the electrical common through a 1.18 Kresistor 510 to provide biasing. The collector of the transistor 492 isconnected to conductor 520 to provide an exponentially decreasingamplification of the signal received on conductor 280.

To provide a continuous bias on conductor 520, the bias circuit 494includes 150 K resistor 516 and a 500 K potentiometer 518. The resistor516 and potentiometer 518 are electrically connected between a source 98of a positive 12 volts and the conductor 520 to permit adjustment of thevoltage drop for application of a current to the ramp generator 278.

In FIG. 16, there is shown a schematic circuit diagram of the rampgenerator 278 (FIG. 9). To form a ramp which varies in slope in a mannerrelated to the output from the exponential amplifier 276 (FIG. 15) forapplication to the flow rate control circuit 32 (FIGS. 2 & 4) the rampgenerator circuit 278 includes a type TL011C current mirror 530 made andsold by Texas Instruments, a 2N3710 NPN transistor 532, a 2N4403 PNPtransistor 534, and a 910 pf capacitor 536. The current mirror 530 hasits input electrically connected to conductor 520 to receive the outputof the exponential amplifier 276 (FIGS. 9 and 15) and its outputelectrically connected to conductor 64 to apply current which decreasesas the motor speed increases from a high output impedance source with again of 1 to draw current from capacitor 536 across to generate anegative going ramp from the capacitor.

The common of the current mirror 530 is electrically connected to thecollector of diode connected transistor 532 through which it conductscurrent. The emitter of the transistor 532 is electrically connected toa source 112 of a negative 8 volts to control the bias on current mirror530. The 2.7 K resistor 538 keeps the voltage at its collector of thetransistor 532 relatively constant at about 7.3 volts regardless of theoperation of the current mirror 530.

To form a ramp from the output of the current mirror 530, conductor 64is electrically connected to its output and to one plate of thecapacitor 536, the other plate of which is electrically connected to theemitter of transistor 534. With this arrangement, the current flowingfrom the output of the current mirror 530 charges capacitor 536 to forma ramp potential on conductor 64.

To reset capacitor 536, the transistor 534 has its collectorelectrically connected to conductor 64 and its base electricallyconnected to the multivibrator circuit 274 (FIGS. 9 & 14) throughconductor 476 so that when the multivibrator provides a negative pulseat the end of a ramp, transistor 534 becomes conducting to dischargecapacitor 536. When transistor 534 becomes nonconducting at the end ofthe negative pulse at its input, the capacitor 536 receives a highimpedance between one plate in conductor 64 and low impedance on theother to be in condition to charge and form a ramp potential onconductor 64 as current flows through the current mirror 530.

The current mirror 530 may be any conventional circuit which results ina complementary current flow from its input. In the preferred embodimentthis is a commercial integrated circuit designated TL011C and sold byTexas Instruments.

In FIG. 17, there is shown a schematic circuit diagram of the linearflow rate control circuit 38 (FIG. 2) having a reference voltage tocurrent converter 540, a summing node 542, a switch 544, and aservoamplifier circuit 546. The reference voltage to current converter540 receives a signal indicating the desired constant flow rate of theinfluent to the chromatographic column on conductor 46 and converts itto a current for application to the summing node 542 where it is summedwith a feedback signal. Upon being gated by the gate 544, this signal isapplied to the main servoamplifier circuit 546 where it is subtractedfrom certain other correction signals for application through conductor62 to the flow rate circuit 32 (FIG. 2).

To provide a feedback signal during the delivery portion of a pumpingstroke, the summing node 542 receives: (1) a current set to representthe desired flow rate from resistor and low pass filter 540; and (2) acurrent from conductor 548 fed back from the motor circuit 30 (FIG. 2)representing the effluent as corrected by the first compensation circuit40 (FIG. 2) in a manner to be described hereinafter.

This current is gated by the analog gate 544 under the control of asignal on conductor 550 to the inverting terminal of the servoamplifier546 where it is summed with a signal from the first compensation circuit40 (FIG. 2) through a conductor 598.

The main servoamplifier 546 receives a signal from the secondcompensation circuit 44 (FIG. 2) through a conductor 554 and thedifference between the two signals is applied to conductor 62. Conductor62 at different times receives compensation circuits on conductors 556to provide servogain and certain compensations such as forcompressibility of the fluids, logic signals on conductor 558, a refillgain correction signal on conductor 560, and a gain from the brakingcircuit on conductor 562.

To process the set point voltage on conductor 46 and apply to summingnode, the reference voltage to current converter 540 includes a 10 Kresistor 570, a 0.1 uf capacitor 572, and a 187 K resistor 574. Theresistor 570 is electrically connected at one end to conductor 46 and atits other end to the electrical common through the capacitor 572 and thesumming node 542 through the resistor 574.

The switch 544 is a type 4016 integrated circuit switch sold by theaforementioned National Semiconductor although any suitableelectronically operated switch may be used. The switch 544 iselectrically connected to be controlled by the first compensationcircuit 40 (FIG. 2).

To compare the signal on conductor 544 fed back from the motortachometer, with the signal on conductor 46 indicating the desirableflow rate, the servoamplifier circuit 546 includes an LM 353differential amplifier 580 sold by National Semiconductor, fourresistors 582, 584, 586 and 590, a 22 pf capacitor 592, and a 1N914diode 594. The resistors are a 470 ohm resistor 582, a 10 K resistor584, a 47 K resistor 586 and a 220 ohm resistor 590. The resistor 582 iselectrically connected at one end to the output of the switch 544 and atits other end to: (1) the inverting input terminal of the amplifier 580to supply a signal thereto representing the flow rate error signal; and(2) conductor 598 electrically connected to the first compensationcircuit 40 (FIG. 2); and (3) to the output of the differential amplifier580 through the capacitor 592.

The output of the amplifier 580 is electrically connected to conductor62 through the resistor 590 and the amplifier has a source 138 of apositive 8 volts connected as one rail at pin 8 and a source 112 of anegative 8 volts connected as a second rail at pin 4. The noninvertinginput terminal of the amplifier is electrically connected to: (1) theelectrical common through the resistor 586; (2) conductor 554 to receivethe feedback pumping rate signal; and (3) a conductor 596 through theforward resistance of the diode 594 and the resistor 584 for placing thepump in the stop mode. Conductor 596 receives a signal from a startcircuit under the control of the system controller 22 (FIG. 1).

In FIG. 18, there is shown a block diagram of the first compensationcircuit 40 (FIG. 2) as it is electrically connected to the linear flowrate control circuit 38 (FIGS. 2 & 17). The first compensation circuit40 (FIG. 2) includes a summing node compensation circuit 600 and aservoamplifier compensation circuit 602 each electrically connected tothe linear flow rate control circuit 38 (FIGS. 2 & 17) at differentlocations, with the summing node compensation circuit 600 beingelectrically connected to the summing mode 542 (FIG. 17) and theservoamplifier compensation circuit 602 being electrically connected tothe servoamplifier inverting input at 598 and at its output as shown at556, 558, 560 and 562 (FIG. 17).

With this arrangement, the speed of the motor is corrected by the rangeof fluid that is flowing, the measured average flow of the influent intothe chromatographic column and for certain factors such as the brakinggain, refill gain, servogain and liquid compensation or for brakingvalues at the input to the servoamplifier

In FIG. 19, there is shown a schematic circuit diagram of the summingnode compensation circuit 600 (FIG. 18) having a range selection circuit608 and coupling circuit shown generally at 604. The switch 608 mayenergize either a high or low voltage levels current to be applied tothe coupling circuit 604 which receives the variable amplitude voltagefrom the frequency to voltage converter 272 (FIGS. 9 and 13) onconductor 280 and converts it to a current applied through conductor 548to the summing node. The magnitude of the current depends on whether ahigh or low range is selected While a switch 608 is shown connected toconductor 630, in the preferred embodiment, a signal from themicro-processor is used to energize the transistor 610 and open switch640. In this specification, a high signal is applied to terminals 628 toselect a one-tenth scale set point and corresponding feedback signalsand terminals 626 or 418 from a low range in which the signals aresubject to less attenuation by a factor of 10.

To provide a larger or smaller current depending on the selection of ahigh or low range, the range selection circuit 608 includes a 2N3704 NPNtransistor 610, 2N3704 NPN transistor 612 and seven resistors which arerespectively a 2.2 K resistor 614, a 2.2 K resistor 616, a 230 ohmresistor 618, a 2.43 K resistor 620, 1 K resistor 622, and a 22 Kresistor 624.

To provide a low range current, the transistor 610 has its emitterelectrically connected to a source 112 of a negative 8 volts, its baseelectrically connected to: (1) a source 94 of a negative 12 voltsthrough the resistor 622; and (3) a source 138 of a positive 8 voltsthrough resistors 618 and 620 in series and has its collectorelectrically connected to: (1) a contact 626 within the switch 608 for alow range current; (2) the base of transistor 612 through resistor 624;and (3) a source 138 of a positive 8 volts through the resistor 616.

The emitter of the transistor 612 is electrically connected to a source112 of a negative 8 volts and its collector is electrically connected toa source 138 of a positive 8 volts through the resistor 614. The switch608 has a movable contact which connects a source of positive potentialto either the low range switch 626 or the high range switch 628, the lowrange switch placing a voltage on conductor 630 and the high rangeswitch placing a voltage on conductor 632.

The conductor 630 is electrically connected through conductor 418 to thefrequency to voltage circuit 272 (FIGS. 9 & 13) to ground the capacitor410 (FIG. 13), thus increasing the amplitude of the output potential.

To convert potential to current for application to the summing node 542(FIG. 17) through conductor 548, the coupling circuit 604 includes ananalog switch 640, a 0.047 uf capacitor 642, three resistors and a 5 Kpotentiometer 652. The three resistors are an 11.5 K resistor 646, a49.9 K resistor 648 and a 4.7 K resistor 650. Conductor 280 from theoutput of the voltage to frequency converter 272 (FIGS. 9 & 13) iselectrically connected to: (1) the input of the switch 640 through thepotentiometer 652 and the resistor 648; and (2) electrical commonthrough the resistor 650 and the capacitor 642. The gate of switch 640is electrically connected to conductors 630 and 418 and its output iselectrically connected to electrical common through the resistor 448 andthe capacitor 642.

In FIG. 20, there is shown a block diagram of the servoamplifiercompensation circuit 602 (FIG. 18), having a braking gain circuit 660, arefill gain circuit 662, a servogain and compensation circuit 664, adelivery logic circuit 666, and an acceleration time generator circuit668. Each of these circuits generates signals relating to the timing ofthe acceleration of the pump motor and applies the signal to the linearflow rate control circuit 38 (FIGS. 2 and 17) through a plurality ofanalog switches. The analog switches are 670, 672, and 674.

For this purpose, the acceleration time generator circuit 668 appliessignals to the delivery logic circuit 666 and to conductor 550 throughone conductor and to the switch 672 through another conductor. Theswitch 670 is controlled by a signal on conductor 72 from the brakecircuit 52 (FIGS. 3 and 5) to apply a brake gain through conductor 560and a servo gain from the servo gain and compensation circuit 664through conductor 558 by opening switch 674. The refill gain is appliedfrom the refill gain circuit 662 upon being opened by a signal from theacceleration time generator circuit 668 indicating a refill cycle.

In FIG. 21, there is shown a schematic circuit diagram of the brakinggain circuit 660, the refill gain circuit 662, and the servo gain andcompensation circuit 664 and their associated switches 670, 672, and 674(FIG. 20) The braking gain circuit 660 is controlled by switch 670, therefill gain circuit 662 is controlled by switch 672 and the servo gainand compensation circuit 664 is controlled by the switch 674 to whichthey are connected to apply currents through conductor 598 to the flowrate control circuit 38 (FIGS. 2 and 17) to change the speed of themotor in accordance with corrections required for braking, refill andservo gain and compensation.

The braking gain circuit 660 includes a 4.7 M resistor 680 electricallyconnected at one end to the output switch 670 and at its other end toconductor 598 to attenuate the signal on conductor 598 during a brakingcycle. Switch 670 has its gate input electrically connected to conductor72 from the brake circuit and its input electrically connected to theconductor 558. The analog switch controls the gain and applies anattenuated voltage of the servo amplifier. The level of the set pointsignal on conductor 46 is level shifted by the 7.5 K resistor 677, thenegative source 112 and the 2.05 K resistor 675 to be applied toconductor 816 when switch 673 is opened.

The refill gain circuit 662 (FIG. 20) includes a 68 K resistor 682 and a1.2 M (megohm) resistor 684. The resistor 682 is electrically connectedto the electrical common at one end and connected to the one lead of theswitch 672 and the resistor 684 is electrically connected at one end toconductor 598 to apply a signal to the linear flow rate control circuit38 (FIG. 2 and 17). Switch 672 has its gate electrically connected toconductor 560 to the delivery logic circuit 666 (FIG. 20) and the seconddrain electrically connected through conductor 556 to the secondcompensation circuit 44 (FIG. 2).

To control servo gain and thus to provide servo stability, the servogain and compensation circuit 664 includes an analog switch 688, two 3.3M resistors 690 and 692, a 180 K resistor 694, a 0.22 uf capacitor 696and a 0.047 uf capacitor 698. One lead of the switch 688 is electricallyconnected through the resistor 690 and the capacitor 696 in series toconductor 598 to apply a compensation signal thereto. The other lead ofthe switch 698 is electrically connected to: (1) the capacitor 696through resistor 690; (2) one lead of the switch 674; (3) conductor 598through the resistor 692 and the capacitor 698 in series.

To control the servogain and compensation circuit, the switch 674 hasits gate electrically connected to the delivery logic circuit 666through conductor 700. With this arrangement, signals from the deliverylogic circuit 666 are applied to the gate of switch 674 to close thisswitch and carry signals from resistors 692 and 694 and switch 688providing the required compensations.

The refill gain circuit 662 (FIG. 20) upon receiving a signal onconductor 556 from the acceleration time generator circuit 668indicating a refill cycle provides a feedback path for the servoamplifier through a resistive network including resistors 682, 684, and685 to conductor 598 and the servo gain and compensation circuit 664closes an additional feedback path for the servo amplifier through aresistance network including a signal applied to switch 688 on conductor702.

In FIG. 22, there is shown a block diagram of the acceleration timegenerator circuit 668 (FIG. 20) having an acceleration timer 710 and anacceleration timer output circuit 712. The acceleration timer 710 iselectrically connected to conductor 76 to receive a refill inceptionsignal, conductor 418 to receive a signal indicating the compressibilityof the fluid being pumped and a signal on conductor 46 indicating theset flow rate.

The acceleration timer 710 processes these signals and applies a signalto the acceleration timer output circuit 712 and to conductors 550 and556 to speed up the motor at the end of fluid delivery at anaccelerating rate to make up for fluid flow that will be lost during atime period before delivery commences again.

The acceleration timer 710 receives a signal indicating the start of therefill cycle and causes a time limit on motor acceleration while thereis no flow so that the cylinder will be filled across the period of timecontrolled by the timer. The motor may also be caused to accelerate in aforward stroke in a manner controlled by the acceleration timer 710 ifthe forward stroke starts during this time period. The time is increasedas the flow rate increases.

In FIG. 23, there is shown a schematic circuit diagram of theacceleration timer 710 having a monostable multivibrator 714, a 2N4403PNP transistor 716 and an analog switch 718. The multivibrator 714 istype 555 sold by National Semiconductor Corporation identified above butany monostable multivibrator may be used provided it is designed to havesatisfactory parameters in a manner known in the art.

To provide an output signal to conductor 724 related to the motoracceleration, the acceleration timer 710 has a time duration circuit720, a connection to lead 418 which carries a signal indicating thecompressibility of the fluid being pumped and an output conductor 724,all of which are electrically connected to the multivibrator 714 so thatthe amplitude adjustment circuit 720 provides correction amplitude forhigh or low range, calibration and compression of liquids.

To trigger the monostable multivibrator 714, conductor 76 from theoutput of the comparator 184 (FIG. 6) drives conductor 724 high atinception of the refill stroke and goes low at the end of the signal anda short time later. It is differentiated by capacitor 762 to trigger themultivibrator to high and maintaining lead 724 high until the timerdrops low under the control of capacitor 150 and current throughtransistor 716 to remove potential from conductor 724.

To permit adjustment of the signal on conductor 744 electricallyconnected to the collector of the transistor 716, the emitter of thetransistor is electrically connected to a source 138 of a positive 8volts through a 16.5 K resistor 746 and a 10 K potentiometer 748. Thetransistor 716 is a type 2N4403 and the adjustment of the potentiometer748 adjusts the current applied to conductor 744 through its collectorso as to permit adjustment of the acceleration time of the motor.

Conductor 744 is electrically connected to pins 6 and 7 and to thesource 112 of a negative 8 volts through a 1 uf timing ramp capacitor150, the source 112 being electrically connected to pin 1 and pins 4 and8 being electrically connected to the source 138 of a positive 8 volts,whereby the time duration of the output pulse width from themultivibrator 714 is adjusted. Pin 5 of the multivibrator 714 iselectrically connected to electrical common through a 0.01 uf capacitor752 and pin 3 is electrically connected to conductor 724 through theforward resistance of a diode 1N914 754 to apply the output to conductor724. The multivibrator 714 is triggered on by the trailing edge of asignal applied through conductors 76A and 76B from the refill initiator.

To trigger the multivibrator 714, the trigger circuit 722 includes a1N914 diode 760, a 0.22 uf capacitor 762, a 1N273 diode 764, a 47 Kresistor 766 and a 3.74 K resistor 768. Conductor 76B is electricallyconnected to conductor 76A through the resistor 768 and to pin 2 of themultivibrator 714 through the capacitor 762. Pin 2 is also electricallyconnected to the source 138 of a positive 8 volts through the resistor766 and the forward resistance of the diode 764. Conductor 76A iselectrically connected to conductor 724 through the forward resistanceof diode 760 and to the cathode of the diode 754 so that, a pulsedifferentiated by capacitor 762 and resistor 766 triggers themultivibrator 714 to apply a potential to conductor 724.

In FIG. 24, there is shown a schematic circuit diagram of theacceleration timer generator output circuit 712 which receives a signalon conductor 724 to establish acceleration across a predetermined periodof time and supplies signals to conductors 686 to close switch 672 (FIG.21) and apply compensation from the refill gain circuit 662 (FIGS. 20 &21) and conductor 550 to open switch 544 (FIG. 17) to disconnectpotential from the summing node 542 (FIG. 17) to the servoamplifier 580(FIG. 17).

To generate a signal for conductor 556, the output circuit includes afirst LM 311 comparator 770 having its inverting input terminalelectrically connected to conductor 724 and its noninverting inputterminal electrically connected to: (1) electrical common through a 2.43K resistor 772; and (2) to a source 112 of a negative 8 volts through a4.7 K resistor 774. The comparator 770 has one rail electricallyconnected to a source 138 of a positive 8 volts and the other railelectrically connected to a source 112 of a negative 8 volts. Itsinverted output is electrically connected to conductor 556 and to asource 112 of a negative 8 volts through a 10 K resistor 776.

To apply a signal to switch 544 (FIG. 17), the acceleration timegenerator output circuit 712 includes a 2N3704 NPN transistor 780 havingits base electrically connected to: (1) conductor 724 through a 15 Kresistor 782; (2) to a source 112 of a negative 8 volts through a 2.2 Kresistor 784. The emitter of the transistor 780 is electricallyconnected to the source 112 of a negative 8 volts and to a source 138 ofa positive 8 volts through a 1 uf capacitor 786. The source 138 of apositive 8 volts is electrically connected to the collector of thetransistor 780 through a 4.7 K resistor 788 and the collector of thetransistor 780 is electrically connected to conductor 550 through a 22 Kresistor 790. Conductor 550 is connected to electrical common through a0.1 uf capacitor 792.

In FIG. 25, there is shown a schematic circuit diagram of the deliverylogic circuit 666 (FIG. 20) having 3 NAND gates 800, 802, and 804,respectively, and a differential amplifier 806. The differentialamplifier 806 has its noninverting input terminal electrically connectedto conductor 556 to receive the output from the main servoamplifier 546(FIG. 17) through a 10 K resistor 810 and a 68 K resistor 812 in series.The inverting input terminal of the differential amplifier 806 iselectrically connected to: (1) conductor 816 to receive a level shiftedset point signal during braking; (2) the electrical common through a 47K resistor 818 and through a 0.1 uf capacitor 820 in parallel to slowthe motor when it is near its constant speed point.

The noninverting input terminal of the amplifier 806 is electricallyconnected to the electrical common through a 220 pf capacitor 822 andthrough the resistor 812 and a 0.1 uf capacitor 824. With thisarrangement, the differential amplifier 806 transmits a negative goingsignal to one input of the two-input NAND gate 804 during braking. Theother input of the NAND gate 804 and conductor 700 are electricallyconnected to the output of a flip-flop comprising NAND gate 802, oneinput of the NAND gate 802 being electrically connected to conductor 550and its other input electrically connected to the output of NAND gate800.

Conductor 550 goes to a low potential at the start of refill, settingthe flip-flop composed of NAND gates 800 and 802. The output of NANDgate 802 is electrically connected to one input of the NAND gate 800 andthe other input is electrically connected to: (1) a source 138 of apositive 8 volts through a 4.7 K resistor 830 and the forward resistanceof a 1N914 diode 832; (2) the source 138 of a positive 8 volts throughthe resistor 830 and a 220 K resistor 834; and (3) the output ofamplifier 806 through the resistor 830, a 0.001 uf capacitor 838 and a10 K resistor 840 in series in the order named. At the end of thebraking period, the servo amplifier output voltage on lead 556 dropsbelow the level shifted setpoint voltage on lead 816. This produces anegative transition at the output of amplifier 806 which resets flipflop 800 and 802 through resistor 840, capacitor 838 and resistor 830.The output of the amplifier 806 is electrically connected to one of thetwo inputs of the NAND gate 804 so as to provide a low output signal forbraking only when the flip-flop including NAND gates 800 and 802 is setand the output of amplifier 806 is high.

In FIG. 26, there is shown a block diagram of the second compensationcircuit 44 having a refill acceleration compensation circuit 850, asample and hold amplifier circuit 852 and a servo voltage multiplier andoffset circuit 854. The refill acceleration compensation circuit 850receives signals on conductor 46 indicating the flow rate and onconductor 418 from the compensation circuit and applies a signal to theramp generator 278 (FIGS. 9 and 16) through conductor 282 when a switch856 is closed by a signal on conductor 700.

To apply a speed-up signal to the servoamplifier, conductor 700 iselectrically connected to gate 858 to open this gate and apply the servogain and compensation to the servo voltage multiplier and offset circuit854. Upon receiving a signal indicating fluid delivery on conductor 862from the delivery logic circuit 666 (FIG. 20), the switch 864 is closedto store the servo feedback signal from the output of the servoamplifier in the sample and hold circuit 852. The sample and holdamplifier circuit 852 is connected to the servo-multiplier and offsetcircuit 850 to be corrected and to apply the signal through gate 858 tothe input 554 of the servoamplifier for acceleration.

In FIG. 27, there is shown a schematic circuit diagram of the refillacceleration compensation circuit 850 having a first analog switch 852,a second analog switch 854 and a 2N3704 NPN transistor 857. Thetransistor 857 applies a signal through switch 864 to conductor 282 tocorrect for the acceleration compensation with a compressibilitycorrection being applied to its base. To apply an acceleration offset tothe transistor 857, conductor 46 carrying set point signal iselectrically connected to: (1) the base of transistor 857 through a 10 Kresistor 868; (2) to the analog switch 854 through the resistor 868; (3)to a source 94 of a negative 12 volts through a 1 K potentiometer gate870, a 500 ohm resistor 872 and a 1 K resistor 874 in series in theorder named.

With this arrangement, the potentiometer 870 may be adjusted to providedifferent base current to the transistor 857. The emitter of thetransistor 857 is electrically connected to a source of a negative 8volts 112 and its collector is electrically connected to the source ofthe switch 864 through a 46.4 K resistor 880 to provide a signal to theoutput conductor 282 upon receiving a signal on conductor 700. Toprovide compressibility compensation, conductor 418 is electricallyconnected to the switch 864 through a 1.8 M resistor 882.

To provide a signal to conductor 520 to modify the rate of accelerationwhich commences at the start of refill when a low range signal isreceived on conductor 626 by the switches 852 and 854, conductor 46 iselectrically connected to the source of the one level of switch 852through: (1) the resistor 858 and a 24.9 K resistor 884; (2) through theresistor 868, a 2.7 K resistor 886 and the resistor 884. Conductor 46 isconnected to the electrical common through the resistor 868 and a 649ohm resistor 888.

In FIG. 28, there is shown a schematic of the sample and hold circuit852 having a switch 890, a storage capacitor 892 and an operationalamplifier 894. The switch 890 is electrically connected to the output ofthe servoamplifier through conductor 556 and to conductor 282 to receivea signal during the delivery portion of the pumping cycle. The switch890 has one lead electrically connected to: (1) one plate of the 0.22 ufstorage and noise filtering capacitor 892 through a 680 K resistor 896and a 3.3 M resistor 898; (2) to the noninverting terminal of theamplifier 894 through the resistors 896 and 898; (3) to the electricalcommon through a 1 uf storage and noise filtering capacitor 900; and (4)to a source 138 of a positive 8 volts through the 22 M resistor 902. Thecapacitor 892 is a 0.22 uf capacitor having one of its plates connectedto the output of the gate 890 and its other connected to electricalground. The capacitors 892 and 900 store a voltage representing thedrive signal to the motor during the delivery portion of the pumping.

The output of the operational amplifier 894 is electrically connected toits inverting input terminal and to a conductor 904 from the servovoltage multiplier and offset circuit 854 (FIG. 26). With this circuitarrangement, a value of potential equivalent to the drive signal to themotor stored on capacitors 892 and 900 and applied with an offset toconductor 904 to the servo voltage multiplier and offset circuit 854.

In FIG. 29, there is shown a schematic circuit diagram of the servovoltage multiplier and offset circuit 854 having an operationalamplifier 910, a first potentiometer 912, an analog switch 914, and asecond potentiometer 916. The potentiometer 916 is electricallyconnected at one end to a source 138 of a positive 8 volts and at theother end to a source 112 of a negative 8 volts to permit selection of apotential to be applied to the source of switch 914 and thepotentiometer 912 is electrically connected at one end to conductor 904of the sample and hold amplifier circuit 852 (FIGS. 26 and 28) through a1 K resistor 918.

The potentiometer 916 is a 10 K potentiometer and the potentiometer 912is a 2 K potentiometer. The other end of the potentiometer 912 iselectrically connected through a 6.19 K resistor 920 and a 100 Kresistor 922 to the inverting input terminal of the operationalamplifier 910. The inverting input terminal of the operational amplifier910 is also electrically connected to conductor 558 through a 100 Kresistor 924 to receive a signal from the output of the servoamplifier.

The output of the amplifier 910 is electrically connected through a 220ohm resistor 926 to one side of the resistor 922 and through a 22 pfcapacitor 928 to the other end of the resistor 922 and to the invertinginput terminal of the amplifier 910. The noninverting input of theamplifier 910 is electrically connected to the electrical common so thatthe input signal from the output of the main servoamplifier on conductor558 is applied to the inverting input terminal of the amplifier 910. Theoutput of the amplifier 910 is applied to one end of the servo voltagemultiplier where its magnitude is adjusted by the servo offset and servovoltage multiplier potentiometers and by the signal on conductor 904 forapplication through the switch 914 and conductor 554 to the input of theservoamplifier, thereby providing a feedback circuit which incorporatesa sample and hold circuit and certain corrections.

When analog switch 914 closes and connects the wiper of potentiometer912 to conductor 554, a negative signal from the sample and hold circuitat 904 is applied through the main servoamplifier 580 (FIG. 17) andinverted in amplifier 910. The signal is transmitted from conductor 904on the output of the amplifier 894 (FIG. 28) in the sample and holdamplifier circuit 852, through the potentiometer 912 and conductor 554to the noninverting input of servoamplifier 580 (FIG. 17) and to theinverting input of operational amplifier 910. The amplifier 910 includesequal input and feedback resistors 922 and 924 establishing a potentialat 927 on the output of the inverter 910 connecting resistors 920, 922and 926 which is inverted but equal to the potential at 558.

The servo amplifier 580 (FIG. 17) is a high gain amplifier and causesthe potential at 554 to be close to zero. Because amplifier 910 is apart of a negative 1 gain inverter, point 927 is the inverted value ofthe output of the servoamplifier at 558. Since the potential at thewiper of potentiometer 912 is not far from zero volts, being not farfrom the potential at 554, the potential at 927 is a multiple of thepotential at 904 established by the voltage divider including theresistance from the wiper to the point 927 and from the wiper to point904. The voltage at 927 is a multiple of the sample and hold voltagewhich is equivalent to the motor drive signal during delivery and theoutput signal at 558 is the inverted value of the potential at 927 torepresent a multiple of the motor drive signal during delivery.

During acceleration, 686 goes high to close 914 connecting it topotentiometer 916. The offset on 916 is set to cause the servo amplifierto go negative when switch 914 closes. Voltage on 554 to servoamplifier, when switch 914 is closed, reaches a balance depending onpotentiometer setting 912. With this arrangement, the servoamplifiergenerates a signal to cause acceleration of the motor until terminatedby the acceleration time generator circuit, causing the total volume offluid per stroke to tend to equalize and thus reduce pulsations ofcurrent through the chromatographic column. The acceleration is relatedto the signal on conductor 558 reflecting the sample and hold voltagestored during delivery

In FIG. 30, there is shown a schematic sectional view of a pump 14(FIG. 1) having a cam 950, a cam follower 952, and a pump head 954. Thecam 950 is mounted to the output shaft of the motor 50 (FIG. 3) forrotation thereby. The cam follower 952 is mounted to move in thedirection of the pump head 954 and the direction of the output shaft asthe cam rotates to provide a reciprocating motion for a piston withinthe pump head 954.

The pump head 954 includes an outlet port 956 and an inlet port 958,closed by pressure-activated valves so that when the piston is movedinwardly in response to the cam follower 952, fluid is drawn into thepump cylinder 960, the outlet port 956 being closed and the inlet port958 being open. Similarly when the piston is moved forwardly, fluid isforced from the outlet port 956 and fluid is blocked from entering orleaving the inlet port 958 by check valves therein. The high pressurepump itself and the electric motor are not part of the inventionthemselves except that the rotatable masses thereof are sufficient toprovide a flywheel effect to the pump itself. This and other flywheelimplements reduce the effect of friction and increases repeatability.Bearings are selected for low friction.

In FIG. 31, there is shown a schematic circuit diagram of a circuit 1000for presetting a liquid flow rate from the pump to adjust the amplitudeof the current on conductor 46 having a keyboard 1002, a clock source1004, an updating circuit 1006, and a current source 1008. The current46, of course, may be set by any analog circuit including a manualpotentiometer in a manner known in the art.

In the preferred embodiment, it is set by a software program utilizingan 8031 microcomputer of the type manufactured by Intel, containing 128bytes of RAM, a serial port and two counter/timers An EPROM in the unitcontains instruction codes for controlling the pump. The softwareprogram for monitoring the current 46 to maintain a constant averageflow rate as follows: ##SPC1##

In addition to a source which may be adjusted by a potentiometer and theuse of a computer as is done in the preferred embodiment, a hardwarecircuit may be used as shown in FIG. 1 in which a keyboard 1002initiates clock pulses from a source 1004 and a value into the updatingcircuit 1006. A source of pulses from the tachometer is applied throughconductor 400 to the updating circuit and the number of tachometerpulses in one cycle of the pump are counted sequentially and comparedwith an idealized number, with the current source being increased if thenumber lags so that the computer averages the amount of flow across acycle of the pump to maintain a constant average flow rate by adjustingthe current source in addition to the other adjustments hereinbeforedescribed.

To monitor the tachometer pulses, the updating circuit includes firstand second counters 1010 and 1012, first and second digital-to-analogconverters 1014 and 1016 and a comparator 1018. The counter 1010 hascounted into it from the clock 1004 the clock pulses in a cycle of thepump before being reset and the clock rate is set to equal the number oftachometer pulses which should be received in one pump cycle. Thecounter 1012 is reset by the same pulse that resets the counter 1010 butcounts the tachometer pulses as they actually occur. Digital-to-analogconverter 1014 generates an analog voltage equivalent to the counts incounter 1010 and digital-to-analog converter 1016 generates an analogsignal equivalent to the counts of counter 1012. The comparator 1018compares the analog outputs from the digital-to-analog converters 1014and 1016 and adjusts the current source 1008 with the signal so as tomaintain a signal on conductor 46 which will compensate for deviationsof flow from the pump from cycle to cycle.

Before operating the pump, it is calibrated to avoid cavitation whilethe motor accelerates from the start of a refill cycle to pull fluidinto the pump until a predetermined period of time has elapsed from thestart of the acceleration. This is accomplished by adjustingpotentiometers 916 and 912 (FIG. 29), 514 (FIG. 15) and 857 (FIG. 27)while pumping water and monitoring the pressure output from stroke tostroke to detect cavitation. The values, which affect the acceleration,when properly set reduce the cavitation and variation in flow rate withpressure variations and may be maintained for maximum operation of thepump.

Once the pump is calibrated, it is operated by setting a flow rate,priming the pump, filling its cylinder and expelling fluid. In expellingthe fluid, near an end portion of the stroke, the pump is run at aconstant speed until it reaches the end of the expulsion stroke, atwhich time a refill signal is generated and the piston begins a refillstroke in a return direction. When it reaches a start of the refillstroke, the pump motor begins to accelerate at the controlled rate andcontinues to accelerate for a predetermined amount of time related tothe operating conditions, at which time it slows to the preset rate forconstant flow.

In setting a flow rate in the preferred embodiment, the flow rate iskeyed into the keyboard and a software circuit retains it, generating aset point signal for application to an analog voltage generator of aconventional type. The analog set point signal controls the flow rate.

The preset flow rate is compared with tachometer pulses generated duringthe forward stroke of the piston of the pump and, if the average pumpingrate is below that preset, the voltage on conductor 46 is increased.

Although a computer is used for this function in the preferredembodiment, it can be accomplished by a hardware circuit such as thatshown in FIG. 1 in which a count representing an ideal tachometer rateis set into a counter 1010 (FIG. 31) and converted to adigital-to-analog signal in the digital-to-analog converter 1014. Thetachometer pulses as they are counted on conductor 400 are alsoconverted to an analog signal in digital-to-analog converter 1016 andthe analog signals are compared to adjust the current source so that abasic linear feedback circuit related to liquid influent flow into thechromatographic column and injector system 18 (FIG. 1) is provided.

Of course, the current for conductor 46 may be set by a simple source ofpotential and variable resistor or by any other technique in which acurrent directly proportional to the flow rate is provided. This currentwill, in general, control through a linear circuit the flow rateregardless of how it is obtained and exert a tendency to maintain itconstant as influent to the chromatographic column.

During a refill cycle and the first part of the cycle forcing fluid outof the pump, the motor 50 (FIG. 3) receives a signal from the nonlinearflow rate control circuit 42 (FIGS. 2 and 9) having a time durationcontrolled by a timer and initiated at a point during the refill cycleand continuing for a time thereafter related to rate of flow which hasbeen set for flow into the chromatographic column. The time ofacceleration is related to the charge on capacitor 150 (FIG. 5) which ismodulated by transistor 716 (FIG. 23) in response partly to the signalon conductor 46 (FIG. 23) from the set point value. The amount ofacceleration is related to the closed loop servo signal which was lastdriving the pump, that value being obtained by a sample and hold circuitelectrically connected to the output of the servoamplifier to store thesignal during the last part of a pumping cycle when the pump is pumpingat a constant rate under closed loop control of a motor speed rotationsignal. The sample and hold amplifier circuit 852 (FIG. 28) stores asignal on a capacitor 900 and 892 (FIG. 28). The rate of acceleration isadjusted by offset and multiplication values during calibration byadjusting potentiometers 916 and 912 (FIG. 29). The signal frompotentiometer 912 is applied as a closed loop control signal to theamplifier 580 (FIG. 17) in which the feedback signal has been closed byanalog switch 914 and the amplifier 910.

With this arrangement, the pump is maintained during a portion of apumping cycle at a constant speed under a tachometer feedback circuitusing analog circuitry and a digital control which adjusts the constantcurrent control for the flow rate. During the refill cycle, the motor isaccelerated continuously while the piston is controlled by a cam toaccelerate and decelerate to zero and then accelerate again, with themotor acceleration terminating at a time controlled by a timer to reducepulsations in flow to a minimum.

From the above description, it can be understood that the pump of thisinvention has several advantages, such as: (1) the time during which noliquid is pumped through the outlet port is low; (2) the pump isrelatively uncomplicated because the acceleration time of the motor istime-limited rather than distance-limited; (3) the pump is able toaccomodate a wider range of flow rates without cavitation; (4) the pumpmaintains an accelerating velocity during the return portion whilerefilling coming to a stop at the end and accelerating upwardly underconstant positive driving of a motor through a cam, with the motorreceiving a continuous accelerating voltage so as to reduce noise whichmight otherwise be caused by inertial effects s the motor speed ischanged; (5) the average flow rate is continuously monitored andadjusted by adjusting a current input signal representing the presetflow rate of fluid; and (6) the flow rate remains constant as pressurevaries.

Although a preferred embodiment of the invention has been described withsome particularity, many modifications and variations are possible inthe preferred embodiment without deviating from the invention.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention may be practiced other than as specificallydescribed.

What is claimed is:
 1. A method of operating a chromatograph in aconstant flow rate mode comprising the steps of:selecting a rate of flowof liquid into a column; representing the flow rate in a digital code interms of a number of pulses for each cycle of a reciprocating pump;measuring the rate of movement of a piston in the reciprocating pumponly in the direction in which it is pumping liquid into achromatographic column; filling the cylinder of the reciprocating pumpin a stroke in a return direction of the piston with effluent to bepumped into the chromatographic column with a motion in the returndirection being controlled by a motor which accelerates starting at atime during the return cycle and ending at a time during a pumpingstroke related to the preset rate of flow into the chromatographiccolumn, wherein the rate of acceleration is controlled from a sample andhold circuit representing the motor current; adjusting the signal in thesample and hold circuit by a value set empirically to avoid cavitation;the signal being applied to a motor driver circuit to accelerate themotor for a predetermined time controlled by a timer set by the rate offlow; and causing the flow from the pump to communicate with the inletof a chromatographic column, whereby a relatively smooth and constantflow of influent into the column is provided.
 2. A method according toclaim 1 further including the steps of:measuring the motor current; andterminating the motor operation when the motor current exceeds apredetermined amount.
 3. A method for controlling the speed of a motorwhich drives a direct displacement reciprocating pump in achromatographic system having a chromatographic column, comprising thesteps of:driving a pump at a constant rate of pumping for a first timeperiod; driving said pump with an acceleration during a second timeperiod which acceleration is related to the constant rate of pumping,whereby the rate of acceleration of said rate of pumping is larger forlarge constant pumping rates than for small constant pumping rates; andcontrolling the rate of acceleration so as to be below the rate at whichcavitation of liquids occurs during a refill portion of a pumping cycleand in which time of acceleration of the pumping action is controlled bya rate of constant flow of liquid to the chromatographic column during aconstant flow portion of a pumping cycle.
 4. A method of operating aliquid chromatographic system having a chromatographic column comprisingthe steps of:setting a flow rate; pumping water through said liquidchromatographic system; during a refill signal of a chromatographic pumpin said chromatographic system, accelerate a motor and locate anacceleration which does not cause cavitation and reduces noise and is ashigh as possible; pump fluid during a delivery stroke at said presetflow rate; at a predetermined time after the end of the delivery strokebegin accelerating the motor and continue accelerating at a rate below apreset maximum rate of cavitation but adjusted for flow rate speed andfor a time duration related to the flow rate; and when said timeduration is completed, terminate acceleration and continue pump motionat said preset flow rate, whereby said acceleration may continue into apumping stroke or terminate below a pumping stroke to minimizepulsations in an output flow from the chromatographic pump.
 5. A methodof operating a chromatographic system having a pump motor andchromatographic column, said pump motor having a rate of acceleration,comprising the steps of controlling the speed of the pump motor during afirst time period at a rate which results in a constant flow rate intothe chromatographic column; andcontrolling the speed of the pump motorin a second time period at a rate which avoids cavitation duringrefilling of the pump and for a time period that is related to the rateof pumping during the first period and in which the motor pumps with apumping cycle portion and a refilling cycle portion for a duration ofthe first time period related to the rate of acceleration and for asecond time period to cause the flow into the pump during the refillingcycle to be equal to the flow out of the pump during the pump cycle. 6.A method according to claim 5 including the steps of:forming a first andsecond signal; said step of forming a second signal includes applying anoutput of a multiplier having a first input, a second input to a meansfor applying positive feedback to a pump motor means; generating asignal proportional to the flow rate of a liquid during a deliverystroke of said pump; applying said signal proportional to the flow rateof the liquid to said first input of said multiplier; and generating anadjustable exponential signal to a value that causes said pump during aperiod of time that starts no earlier than the beginning of a refillstroke to cause fluid flow in communication with a high-pressure pump ata rate that does not cause cavitation.
 7. A method in accordance withclaim 6 comprising:applying a power means to said pump motor means froma pulse-width modulator; applying a first input to said pulse-widthmodulator from said means for generating a first signal; applying asecond input signal to said power means from a means for generating asecond positive feedback signal; and generating a negative feedbacksignal which is a velocity signal fed back during at least a portion ofthe pumping cycle, whereby a delivery rate is constant during saidportion.
 8. A method in accordance with claim 7 comprising the stepsof:applying a first signal related to said preset flow rate to saidpulse-width modulator; transmitting a ramp signal related to velocityfeedback to said pulse-width modulator; and varying the first and secondsignals linearly with velocity feedback in a delivery mode andnonlinearly during a refill mode.
 9. A method in accordance with claim 8further including the step of starting a refill cycle at a time relatedto a negative velocity feedback means.
 10. A method in accordance withclaim 9 further including the step of compensating for a signalelectrically connected in circuit with a means for starting a refillcycle and a first velocity negative feedback control circuit.
 11. Amethod in accordance with claim 10 including the step of generating asignal indicating motor speed from said negative velocity feedbackcircuit means.
 12. A method in accordance with claim 11 comprisingdriving the motor with said pulse-width modulator to supply power to amotor; andtransmitting pulse-width-modulated pulses to a driver circuitinversely related in width to the steepness of said ramp signal appliedto a conductor and directly related to an amplitude of a signal appliedto a first conductor, whereby said means for driving said motor providespulses to maintain a constant speed in one mode and to provide constantacceleration in another mode.
 13. A method in accordance with claim 12including the steps of:applying a first signal to a comparator during apumping mode; varying said first signal in amplitude with deviationsfrom a preset velocity of pumping; and applying a second signal which isa periodic ramp wherein the comparator provides a pulse the width ofwhich is directly related to the comparison between said first signaland second signal, whereby a pulse width is generated which varieslinearly in width with deviations from a preset pulse width.
 14. Amethod in accordance with claim 13 including the step of varying saidsecond signal in rate of rise in accordance with a preset accelerationsignal, whereby the pulse width of said driver circuit increases at apreset rate so as to provide acceleration of said pump motor.
 15. Amethod in accordance with claim 14 including the step of feeding back asignal from a tachometer means; and applying an output signalproportional to the velocity of said motor to a frequency-to-voltageconverter.
 16. A method in according with claim 15 further including thestep of adjusting the amplitude of said signal related to the rate ofpumping of said motor; whereby said flow rate may be adjusted to avoidcavitation.
 17. A method according to claim 16 further including thestep of generating periodic timing signals and applying them to a meansfor generating a ramp signal, whereby the timing of said ramp signal iscontrolled.
 18. A method in accordance with claim 17 in which amultivibrator provides pulses for resetting a ramp generator and forresetting said means for driving said motor.
 19. A method in accordancewith claim 18 in which said signal indicating motor speed is amplifiednonlinearly, whereby a ramp is provided which increases at a raterelated to a rate of pumping.